From: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date: Thu, 29 Mar 2018 09:27:29 +0000 (+0200)
Subject: Fix a possible crash in BN_from_montgomery_word
X-Git-Tag: OpenSSL_1_1_1-pre4~14
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=f91e026e38321d0c154f535ecd5af09e424e7f1b;p=oweals%2Fopenssl.git

Fix a possible crash in BN_from_montgomery_word

Thanks to Darovskikh Andrei for for reporting this issue.

Fixes: #5785

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5793)
---

diff --git a/crypto/bn/bn_mont.c b/crypto/bn/bn_mont.c
index c882891d5e..362390a353 100644
--- a/crypto/bn/bn_mont.c
+++ b/crypto/bn/bn_mont.c
@@ -95,6 +95,8 @@ static int BN_from_montgomery_word(BIGNUM *ret, BIGNUM *r, BN_MONT_CTX *mont)
 
     /* clear the top words of T */
     i = max - r->top;
+    if (i < 0)
+        return 0;
     if (i)
         memset(&rp[r->top], 0, sizeof(*rp) * i);
 
diff --git a/test/bntest.c b/test/bntest.c
index d6696e672e..d5b5e0494e 100644
--- a/test/bntest.c
+++ b/test/bntest.c
@@ -408,9 +408,21 @@ static int test_modexp_mont5(void)
     BN_free(b);
     b = BN_dup(a);
     BN_MONT_CTX_set(mont, n, ctx);
-    BN_mod_mul_montgomery(c, a, a, mont, ctx);
-    BN_mod_mul_montgomery(d, a, b, mont, ctx);
-    if (!TEST_BN_eq(c, d))
+    if (!TEST_true(BN_mod_mul_montgomery(c, a, a, mont, ctx))
+            || !TEST_true(BN_mod_mul_montgomery(d, a, b, mont, ctx))
+            || !TEST_BN_eq(c, d))
+        goto err;
+
+    /* Regression test for bug in BN_from_montgomery_word */
+    BN_hex2bn(&a,
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
+    BN_hex2bn(&n,
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
+    BN_MONT_CTX_set(mont, n, ctx);
+    if (!TEST_false(BN_mod_mul_montgomery(d, a, a, mont, ctx)))
         goto err;
 
     /* Regression test for bug in rsaz_1024_mul_avx2 */